It says that $\vec{F}_2$ and $\vec{F}_4$ have the same magnitude but different direction, which makes the net force zero, but I don't understand why the net torque becomes zero.
F1 and F3 is perpendicular to the field which F2 and F4 isn't

It says the reason why it's zero is because the line of action is through the center of the loop.

How can this be a problem? Can't it just flip the other way as well????

The image has the text "a torque acts to align the normal vector $\vec n$ with the direction of the field". Where does it say the torque is zero? Please refine your question.
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Alfred CentauriJun 23 '13 at 22:12